1. Field of the Invention
The invention relates to fiber-optics refractive index detecting devices and the use of such devices as detectors in liquid chromatography.
2. Description of the prior art
U.S. Pat. No. 2,569,127 describes a fiber-optics apparatus designed to continuously measure and record the refractive index of a fluid substance, and to control the properties or characteristics of the fluid in response to variations in refractive index.
U.S. Pat. No. 2,964,993 describes a fiber-optics apparatus for automatically measuring specific gravity and/or composition of a fluid which apparatus relies on the changes in the conductivity of light passing through a radiant energy guide, such as an artificial sapphire rod, as a consequence of changes in the absorption characteristics and index of refraction. The apparatus has a null balanced indicator which operates by changing the position of the light source along the waveguide.
U.S. Pat. No. 3,017,802 describes a fiber-optics apparatus which measures the index of refraction and absorption characteristics of a substance surrounding a radiant energy guide or rod member and provides for the measurement also of a reference fluid.
U.S. Pat. No. 3,311,014 describes a fiber-optics apparatus which provides a unitary light-to-electrical voltage transforming apparatus for selectively adjusting the entry angle at which the central longitudinal axis of the light cone enters an edge portion of one end of a light transmitting fluid immersed probe so that only one probe need be used to measure many different index of refraction ranges of fluids. A reference cell is provided to maintain at a set value the intensity of the light transmitted to the probe.
U.S. Pat. No. 3,370,502 describes a fiber-optics absorption cell having a rod with a cell surrounding the rod, radiant energy directed at one end of the rod and passing down the rod with frustrated multiple internal reflection. The rod may have its effective length adjustable so as to permit nulling or calibration.
U.S. Pat. No. 3,513,319 describes a fiber-optics refractometer comprising a bundle of radiation transparent tubes extending from a radiation source to a detector. The central section of the tubes extend through a vessel which contains the fluid being analyzed. The outer sections of the tubes are clad with a material having lower refractive indices than the tubes. A differential refractometer employing two such tube bundles and vessels is also provided. The refractometer is used as a detector in a chromatographic analyzer. The use of a coherent radiation source is stated to be particularly effective. A reference fluid is provided in one embodiment.
U.S. Pat. No. 3,619,068 describes a fiber-optics refractometer formed by a housing having two intersecting passages. The fluid to be tested is passed through the first passage, and a radiation beam is passed through the second. A bundle of light tubes is positioned in the second passage so that one end of the bundle is disposed in the test fluid at an angle with the axis of the tube bundle. A radiation detector measures the radiation passed through the tube bundle. The refractometer is particularly designed as a low-cost detector for use in liquid chromatography.